Sphygmomanometer, and method and device for measuring blood pressure

ABSTRACT

A sphygmomanometer includes: a bag-shaped sensing cuff to be worn to wrap a measurement site; a back plate disposed on the sensing cuff along a surface opposite to the measurement site; a pressing member for pressing the back plate toward the measurement site; and a blood-pressure calculating part calculating a blood pressure based on a pressure of a fluid stored in the sensing cuff. Regarding a longitudinal direction perpendicular to a circumferential direction of the measurement site to be wrapped by the sensing cuff, a surface facing the measurement site in edge potions on both sides in a width direction along the longitudinal direction of the back plate is curved in a direction away from the measurement site toward tips.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation application of International Application No. PCT/JP2017/042370, with an International filing date of Nov. 27, 2017, which claims priority of Japanese Patent Application No. 2016-256030 filed on Dec. 28, 2016, the entire content of which is hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a sphygmomanometer and, more particularly, to a sphygmomanometer comprising a belt worn to wrap a measurement site and a main body equipped with a pump. The present invention also relates to a blood-pressure measurement method for measuring a blood pressure at a measurement site. The present invention further relates to a device having a blood-pressure measurement function.

BACKGROUND ART

For example, as disclosed in Patent Document 1 (Japanese Laid-Open Patent Publication No. 11-309119), a conventionally known sphygmomanometer of this type has a cuff wound around a wrist that is a measurement site, and a main body integrally attached to the cuff. This sphygmomanometer includes, in a strap-shaped belt, a bag-shaped blood-pressure measurement cuff compressing an artery, an intervening member disposed on the outside of the blood-pressure measurement cuff, and a bag-shaped pressing cuff disposed on the outside of the intervening member, and is configured to detect a pressure in the blood-pressure measurement cuff with a pressure sensor mounted on the main body. At the time of blood pressure measurement, a predetermined amount of air for pressurization is supplied from a pump mounted on the main body to the blood-pressure measurement cuff while the belt is worn to wrap the wrist, and subsequently, air is also supplied to the pressing cuff to compress the artery of the wrist (radial artery, ulnar artery). Based on an output of the pressure sensor, a blood pressure measurement value is calculated by an oscillometric method. In this sphygmomanometer, a predetermined amount of air is supplied to the blood-pressure measurement cuff, and a force for sufficiently compressing a living body site is achieved by the intervening member and the pressing cuff, so that a feeling of oppression or discomfort is eliminated while the cuff is worn.

SUMMARY OF THE INVENTION

A recent rise in health consciousness is leading to a growing need for measuring a blood pressure with a sphygmomanometer (blood-pressure measurement cuff) always worn on the wrist. In this case, it is desirable to make a width-direction dimension of a cuff (a dimension in a direction along a longitudinal direction of the wrist) as small as possible from the viewpoints of appearance, wearing comfort, etc.

If the width-direction dimension of the cuff is set as small as, for example, about 25 mm, it is important from the viewpoint of blood pressure measurement accuracy to make a pressing force to the measurement site (wrist) uniform in the width direction of the cuff. In this regard, the present inventor found through experiments that stress concentration occurs at a position of the measurement site corresponding to an edge portion in the width direction of a plate-shaped intervening member and makes the pressing force higher. Therefore, if the dimensions of the intervening member and the blood-pressure measurement cuff are equal in the width direction, the pressing force to the blood-pressure measurement cuff has a deviation caused by the stress concentration at a skin surface position and a blood vessel position of the measurement site and becomes higher in the edge portion as compared to a central portion in the width direction. As a result, the pressing force of the blood-pressure measurement cuff to the measurement site is not uniform in the width direction, causing a problem that a measurement error occurs in a blood pressure value.

Therefore, an object of the present invention is to provide a sphygmomanometer, a blood-pressure measurement method, and a device capable of accurately measuring a blood pressure even when the blood pressure is measured by pressing a blood-pressure measurement cuff via an intervening member.

To achieve the object, a sphygmomanometer of the present disclosure is a sphygmomanometer comprising:

a bag-shaped sensing cuff to be worn to wrap a measurement site;

a back plate disposed on the sensing cuff along a surface opposite to the measurement site;

a pressing member for pressing the back plate toward the measurement site; and

a blood-pressure calculating part calculating a blood pressure based on a pressure of a fluid stored in the sensing cuff, wherein

regarding a longitudinal direction perpendicular to a circumferential direction of the measurement site to be wrapped by the sensing cuff, a surface facing the measurement site in edge potions on both sides in a width direction along the longitudinal direction of the back plate is curved in a direction away from the measurement site toward tips with the edge portions on both sides respectively gradually becoming thinner toward the tips.

As used herein, the term “measurement site” refers to a site through which an artery passes. The measurement site may be, for example, an upper limb such as a wrist and an upper arm, or a lower limb such as an ankle and a thigh.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:

FIG. 1 is a view showing an appearance of a sphygmomanometer of an embodiment of the present invention with a belt fastened as viewed obliquely.

FIG. 2 is a view showing the appearance of the sphygmomanometer with the belt released as viewed obliquely.

FIG. 3B is a view showing a planar layout when a cuff structure of FIG. 2 is in a developed state with an inner circumferential surface on the forefront. FIG. 3A is a view showing a cross section taken along a line IIIA-IIIA of FIG. 3B as viewed in a direction of arrows.

FIG. 4A is an enlarged view showing the vicinity of a tip portion of the cuff structure of FIG. 3B. FIG. 4B is a view showing a cross section taken along a line IVB-IVB of FIG. 4A as viewed in a direction of arrows.

FIG. 5A is a view showing a planar layout of a pressing cuff included in the cuff structure. FIG. 5B is a view showing a planar layout of a back plate included in the cuff structure with the pressing cuff in the background.

FIG. 6 is a view showing a back side of a main body of the sphygmomanometer as viewed obliquely.

FIG. 7 is a view showing the back side of the main body in a disassembled state with a back lid removed, including a curler included in the cuff structure.

FIG. 8 is a view showing the inside of the main body as viewed obliquely from above.

FIG. 9 is a view showing the inside of the main body as viewed obliquely from below.

FIG. 10 is a diagram showing a block configuration of a control system of the sphygmomanometer.

FIG. 11 is a diagram showing an operation flow when a user performs a blood-pressure measurement method of an embodiment to measure a blood pressure with the sphygmomanometer.

FIG. 12 is a diagram showing a flow of a process when the user wears the sphygmomanometer on the left wrist.

FIG. 13A is a perspective view showing a form when the user wears the cuff structure on the left wrist by using the right hand.

FIG. 13B is a perspective view showing a form when the user wraps the left wrist and the cuff structure with a belt together by using the right hand.

FIG. 13C is a perspective view showing a form when the sphygmomanometer is worn on the left wrist of the user.

FIG. 14 is a view showing a cross section perpendicular to the left wrist while the sphygmomanometer is worn on the left wrist of the user.

FIG. 15A is a view showing a cross section (corresponding to a cross section taken along a line XVA-XVA of FIG. 14 as viewed in a direction of arrows) of a portion through which a tendon of the left wrist passes in a pressurized state.

FIG. 15B is a view showing a cross section (corresponding to a cross section taken along a line XVB-XVB of FIG. 14 as viewed in a direction of arrows) of a portion through which the radial artery of the left wrist passes in the pressurized state.

FIG. 16 is a view exemplarily showing a pressure Pc and a pulse wave signal Pm of a sensing cuff detected by a second pressure sensor mounted on the main body.

FIG. 17 is a view showing a blood-pressure measurement error when water is used as a pressure-transmitting fluid stored in the sensing cuff and an amount of the water stored in the sensing cuff is variably set.

FIG. 18 is a scatter diagram of a relationship between a reference blood pressure value and a blood-pressure measurement error when the amount of the water stored in the sensing cuff is variably set to “small water amount”=0.16 ml, “appropriate amount”=0.3 ml, “large water amount”=0.8 ml for multiple users.

FIG. 19 is a schematic view showing a dimensional relationship in a width direction of the curler, the pressing cuff, the back plate, and the sensing cuff.

FIG. 20A is a view showing results of simulations of pressure distribution on a skin surface and pressure distribution around blood vessels when a pressure of 300 mmHg is applied to the back plate by the pressing cuff.

FIG. 20B is a view showing results of simulations of pressure distribution on a skin surface and pressure distribution around blood vessels when a pressure of 300 mmHg is applied to the skin surface by the pressing cuff.

FIG. 21 is a schematic view showing the back plate in which a surface facing the measurement site in edge portions on both sides in the width direction is curved in a direction away from the measurement site toward tips.

FIG. 22 is a schematic view showing the back plate in which a surface facing the measurement site in the edge portions on both sides in the width direction is curved in a direction away from the measurement site.

FIG. 23 is a view showing results of simulations of pressure distribution on a skin surface and pressure distribution around blood vessels when a pressure of 300 mmHg is applied to the back plate of FIG. 21 by the pressing cuff.

FIG. 24 is a diagram showing results of simulations of pressure distribution on a skin surface and pressure distribution around blood vessels when a pressure of 300 mmHg is applied to the back plate of FIG. 22 by the pressing cuff.

FIG. 25 is a schematic view when width-direction dimensions are made equal between the sensing cuff and the back plate in which a surface facing the measurement site in edge portions on both sides in the width direction is curved in a direction away from the measurement site toward tips.

DESCRIPTION OF EMBODIMENT

Embodiments of the present invention will now be described in detail with reference to the drawings.

(Configuration of Sphygmomanometer)

FIG. 1 shows an appearance of a sphygmomanometer (generally denoted by reference numeral 1) of an embodiment of the present invention with a belt 2 fastened as viewed obliquely. FIG. 2 shows the appearance of the sphygmomanometer 1 with the belt 2 released as viewed obliquely.

As shown in these figures, the sphygmomanometer 1 roughly includes a main body 10, the belt 2 extended from the main body 10 and to be worn to wrap a measurement site (in this example, as shown in FIG. 13C described later, a left wrist 90 is supposed to be the measurement site), and a strap-shaped cuff structure 20 having one end 20 f attached to the main body 10. The dimension in a width direction X of the belt 2 is set to 29 mm in this example. The thickness of the belt 2 is set to 2 mm in this example.

In this example, the main body 10 has a substantially short cylindrical-shaped case 10B, a circular glass 10A attached to an upper portion (in FIGS. 1 and 2) of the case 10B, and a back lid 10C (see FIG. 6) attached to a lower portion of the case 10B. A side surface of the case 10B is integrally provided with respective pairs of projecting lugs 10B1, 10B2; 10B3, 10B4 on the right and left sides (in FIGS. 1 and 2) for attaching the belt 2.

A display 50 constituting a display screen is disposed inside the glass 10A of the upper portion of the case 10B. The side surface on the near side (in FIGS. 1 and 2) of the main body 10 is provided with a measurement switch 52A for giving an instruction for starting or stopping a blood pressure measurement, a home switch 52B for returning the display screen of the display 50 to a predetermined home screen, and a record calling switch 52C for instructing the display 50 to display past measurement records of blood pressure, activity amount, etc. (these switches are collectively referred to as an operation part 52). Additionally, blood-pressure measurement elements including a pump 30 are mounted inside the main body 10 (described in detail later). In this example, the sphygmomanometer 1 has functions of an activity amount meter and a pulsometer. Therefore, the sphygmomanometer 1 is configured as a multifunctional device having a form of a watch-type wearable device. The main body 10 is small-sized and thinly formed so as not to interfere with daily activities of a user.

As can be seen clearly from FIG. 2, the belt 2 has a strap-shaped first belt part 3 extending from the main body 10 to one side (right side in FIG. 2) in one direction and a strap-shaped second belt part 4 extending from the main body 10 to the other side (left side in FIG. 2) in opposite direction. A root portion 3 e of the first belt part 3 on the side closer to the main body 10 is attached pivotally as indicated by a double arrow A to the lugs 10B1, 10B2 of the main body 10 via a coupling rod 7 (known spring rod) extending in the width direction X of the belt. Similarly, a root portion 4 e of the second belt part 4 on the side closer to the main body 10 is attached pivotally as indicated by a double arrow B to the lugs 10B3, 10B4 of the main body 10 via a coupling rod 8 (known spring rod) extending in the width direction X of the belt.

A buckle 5 is attached to a tip portion 3 f of the first belt part 3 on the side far from the main body 10. The buckle 5 is of a known type and includes a substantially U-shaped frame-shaped body 5A, a prong 5B, and a coupling rod 5C extending in the width direction X of the belt. The frame-shaped body 5A and the prong 5B are both attached pivotally as indicated by a double arrow C to the tip portion 31 of the first belt part 3 on the side far from the main body 10 via the coupling rod 5C. A ring-shaped belt holding portions 6A, 6B are integrally disposed between the tip portion 31 and the root portion 3 e of the first belt part 3 at positions predefined in a longitudinal direction of the first belt part 3 (corresponding to a circumferential direction Y of the left wrist 90). An inner circumferential surface 3 a of the first belt part 3 does not protrude toward the inner circumferential side at the positions of the belt holding portions 6A, 6B and is basically formed flat (locally, although curved as a whole). Therefore, the belt 2 is designed to uniformly wrap and bind the outer circumferential side of the cuff structure 20.

Multiple small holes 4 w, 4 w . . . each penetrating in the thickness direction of the second belt part 4 are formed in the second belt part 4 between the root portion 4 e and a tip portion 4 f on the side far from the main body 10. When the first belt part 3 and the second belt part 4 are fastened, a portion leading to the tip portion 4 f of the second belt part 4 is passed through the frame-shaped body 5A of the buckle 5, and the prong 5B of the buckle 5 is inserted through any one of the multiple small holes 4 w, 4 w . . . . As a result, the first belt part 3 and the second belt part 4 are fastened as shown in FIG. 1.

In this example, the first belt part 3 and the second belt part 4 constituting the belt 2 are made of a plastic material flexible in the thickness direction and substantially inelastic in the longitudinal direction (corresponding to the circumferential direction Y of the left wrist 90). Therefore, the belt 2 can easily wrap and bind the outer circumferential side of the cuff structure 20 at the time of wearing and can assist compression of the left wrist 90 at the time of blood pressure measurement described later. The first belt part 3 and the second belt part 4 may be made of a leather material. The frame-shaped body 5A and the prong 5B constituting the buckle 5 are made of a metal material in this example or may be made of a plastic material.

As shown in FIG. 2, the cuff structure 20 includes a curler 24 disposed on an outermost circumference, a pressing cuff 23 disposed along an inner circumferential surface of the curler 24, a back plate 22 serving as a reinforcing plate disposed along an inner circumferential surface of the pressing cuff 23, and a sensing cuff 21 disposed along an inner circumferential surface of the back plate 22. In this embodiment, the belt 2 described above, the curler 24, and the pressing cuff 23 function as pressing members capable of generating a pressing force toward the wrist, and the back plate 22 is pressed by these pressing members toward the wrist that is a measurement site so as to compress the wrist via the sensing cuff 21 interposed between the back plate 22 and the wrist.

FIG. 3B shows a planar layout when the cuff structure 20 of FIG. 2 is in a developed state with an inner circumferential surface 20 a on the forefront. FIG. 3A shows a cross section taken along a line IIIA-IIIA of FIG. 3B as viewed in a direction of arrows. FIG. 4A shows an enlarged view of the vicinity of a tip portion of the cuff structure 20 of FIG. 3B. FIG. 4B shows a cross section taken along a line IVB-IVB of FIG. 4A as viewed in a direction of arrows. FIG. 5A shows a planar layout of the pressing cuff 23. FIG. 5B shows a planar layout of the back plate 22 with the pressing cuff 23 in the background.

As shown in FIGS. 3A and 3B, the curler 24, the pressing cuff 23, the back plate 22, and the sensing cuff 21 each have a strap shape elongated in one direction (Y direction). In this example, the curler 24 has a dimension in the width direction X set to W1=28 mm, the pressing cuff 23 has a dimension in the width direction X (excluding welded edge portions on both sides) set to W2=25 mm, the back plate 22 has a dimension in the width direction X set to W3=23 mm, and sensing cuff 21 has a dimension in the width direction X (excluding welded edge portions on both sides) set to W4=15 mm. Details of a relationship between the dimension in the width direction X of the back plate 22 and the dimension in the width direction X of the sensing cuff 21 will be described later. The curler 24 has a dimension in the longitudinal direction Y (excluding a root portion 24 f attached to the main body 10) set to L1=148 mm, the pressing cuff 23 has a dimension in the longitudinal direction Y set to L2=140 mm, the back plate 22 has a dimension in the longitudinal direction Y set to L3=114 mm, and the sensing cuff 21 has a dimension in the longitudinal direction Y set to L4=110 mm.

As can be seen from FIGS. 4A and 4B, the sensing cuff 21 includes a first sheet 21A on the side in contact with the left wrist 90 and a second sheet 21B facing the first sheet 21A, and is formed into a bag shape by bringing circumferential edge portions 21 m of the first and second sheets 21A, 21B into close contact with each other by welding. In this example, as shown in FIG. 4B, sags 21 r, 21 r extending along the longitudinal direction Y of the sensing cuff 21 are disposed in a natural state at positions leading to the edge portions 21 m, 21 m on both sides in the width direction X of the sensing cuff 21. Additionally, as shown in FIG. 4A, sags 21 r extending along the width direction X of the sensing cuff 21 are disposed in the natural state in the first sheet 21A at positions leading to the edge portions 21 m on both sides in the longitudinal direction Y of the sensing cuff 21 (only a leading end side is shown in FIG. 4A). The sags 21 r as described above may be formed by a known method, for example, when the circumferential edge portions 21 m of the first and second sheets 21A, 21B are welded and brought into close contact with each other. As can be seen from FIGS. 3A and 3B, to an end portion on the root side (+Y side) in the longitudinal direction Y of the sensing cuff 21, a flexible tube 38 is attached for supplying a pressure-transmitting fluid (air in this example) to the sensing cuff 21 or discharging the pressure-transmitting fluid from the sensing cuff 21. The material of the first and second sheets 21A, 21B is an elastic polyurethane sheet (thickness t=0.15 mm) in this example. The inner circumferential surface 20 a of the cuff structure 20 is made up of the first sheet 21A of the sensing cuff 21.

As can be seen from FIGS. 4A and 4B, the pressing cuff 23 includes two fluid bags 23-1, 23-2 stacked in the thickness direction. Each of the fluid bags 23-1, 23-2 is formed by welding circumferential edge portions 23 m 1, 23 m 2 of two elastic polyurethane sheets (thickness t=0.15 mm) faced each other. As shown in FIG. 5A, the dimension in the longitudinal direction Y of the fluid bag 23-1 on the inner circumferential side is set slightly smaller than the dimension (L2) in the longitudinal direction Y of the fluid bag 23-2 on the outer circumferential side. To an end portion on the root side (+Y side) in the longitudinal direction Y of the fluid bag 23-2 on the outer circumferential side, a flexible tube 39 is attached for supplying a pressure-transmitting fluid (air in this example) to the pressing cuff 23 or discharging the pressure-transmitting fluid from the pressing cuff 23. Multiple (four in this example) through-holes 23 o, 23 o . . . are formed between the fluid bag 23-1 on the inner circumferential side and the fluid bag 23-2 on the outer circumferential side adjacent thereto. Therefore, a pressurizing fluid (air in this example) can flow between the two fluid bags 23-1, 23-2 through the through-holes 23 o, 23 o . . . . As a result, when the pressing cuff 23 in a worn state receives the supply of the pressurizing fluid from the main body 10 side through the flexible tube 39, the two stacked fluid bags 23-1, 23-2 expand to compress the left wrist 90 as a whole.

The back plate 22 is made up of a plate-shaped resin (polypropylene in this example) having a thickness of about 1 mm in this example. As can be seen from FIGS. 3A and 3B, the back plate 22 is disposed on the sensing cuff 21 along the surface opposite to the measurement site. The back plate 22 extends in a strap shape beyond the length of the sensing cuff 21 in the longitudinal direction Y (corresponding to the circumferential direction of the left wrist 90). Therefore, the back plate 22 can function as a reinforcing plate to transmit the pressing force from the pressing cuff 23 to an entire region in the longitudinal direction Y of the sensing cuff 21 (corresponding to the circumferential direction of the left wrist 90). As can be seen from FIGS. 4A and 5B, multiple grooves 22 d 1, 22 d 2 having V-shaped or U-shaped cross sections and extending in the width direction X are disposed on an inner circumferential surface 22 a and an outer circumferential surface 22 b of the back plate 22 and parallelly separated from each other in the longitudinal direction Y. In this example, the grooves 22 d 1, 22 d 2 are disposed at the same positions corresponding to each other between the inner circumferential surface 22 a and the outer circumferential surface 22 b of the back plate 22. As a result, the back plate 22 is made thinner and easier to bend at the positions of the grooves 22 d 1, 22 d 2 as compared to the other positions. Therefore, when the user brings the left wrist 90 and the cuff structure 20 into a state of being wrapped with the belt 2 together at the time of wearing (step S22 in FIG. 12 described later), the back plate 22 does not prevent the cuff structure 20 from curving along the circumferential direction Y of the left wrist 90.

The curler 24 is made up of a plate of resin (polypropylene in this example) having certain degrees of flexibility and hardness and a thickness of about 1 mm in this example. As can be seen from FIGS. 3A and 3B, the curler 24 in the developed state extends in a strap shape beyond the length of the pressing cuff 23 in the longitudinal direction Y (corresponding to the circumferential direction of the left wrist 90). As shown in FIG. 7, the curler 24 has a curved shape along the circumferential direction Y surrounding the left wrist 90 in the natural state. As a result, the shape of the cuff structure 20 in the natural state is kept curved along the circumferential direction Y of the left wrist 90 as shown in FIG. 2.

A circumferential edge portion of the inner circumferential surface 22 a of the back plate 22 and a circumferential edge portion of an inner circumferential surface 24 a of the curler 24 are provided with respective curves 22 r, 24 r curved in a direction away from the measurement site (the left wrist 90 in this example). This prevents the user from having a feeling of discomfort due to wearing of the cuff structure 20.

As shown in FIG. 6, a back lid 10C is disposed on the back side of the main body 10. The back lid 10C has four through-holes 10C1, 10C2, 10C3, 10C4 and is fixed to the back side of the case 10B by screws not shown through the through-holes 10C1, 10C2, 10C3, 10C4. Intake/exhaust holes 10Bo, 10Bo . . . with filters are disposed in a portion hidden by the root portion 3 e of the first belt part 3 in the side surface of the case 10B (the same applies to a portion hidden by the root portion 4 e of the second belt 4). This allows air to flow between the inside and the outside of the case 10B while a water-resistant function is implemented.

FIG. 7 shows the back side of the main body 10 in a disassembled state with the back lid 10C removed, including a curler 24 described above. In the case 10B of the main body 10, an inner case member 11 for mounting the blood-pressure measurement elements is stored. The back side of the inner case member 11 has an annular groove 11 d formed to surround a periphery of a protrusion 11 p. A ring 24 o having a shape corresponding to the annular groove lid is formed at the root portion 24 f of the curler 24. When the main body 10 is assembled, the ring 24 o of the root portion 24 f of the curler 24 is fitted into the annular groove lid of the inner case member 11 (at the same time, the ring 24 o is fitted to the protrusion 11 p of the inner case member 11). The root portion 24 f of the curler 24 is then sandwiched between the back side of inner case member 11 and the back lid 10C of the main body 10, while overlapping with two flow-path forming members (a first flow-path forming member 390 and a second flow-path forming member 380) described later.

As a result, as shown in FIG. 2, the one end 20 f of the cuff structure 20 (the root portion 24 f of the curler 24) is attached to the main body 10. The other end 20 e of the cuff structure 20 (a tip portion 24 e of the curler 24) is a free end. Consequently, the cuff structure 20 faces the inner circumferential surfaces 3 a, 4 a of the belt 2 and can be separated from the inner circumferential surfaces 3 a, 4 a.

When the cuff structure 20 is attached to the main body 10 in this way, the one end 20 f of the cuff structure 20 is reliably held by the main body 10. At the time of maintenance service, the cuff structure 20 can be replaced for the main body 10 independently of the belt 2 by opening the back lid 10C of the main body 10. The dimension in the longitudinal direction Y (corresponding to the circumferential direction of the left wrist 90) of the cuff structure 20 may be set to an optimum dimension independently of the belt 2.

In the sphygmomanometer 1, the main body 10 and the belt 2 are formed separately from each other, and the belt 2 is attached to the main body 10, and therefore, the belt 2 can be replaced for the main body 10 independently of the cuff structure 20 at the time of maintenance service.

The first flow-path forming member 390 shown in FIG. 7 is made up of two sheet plates 391, 392 facing each other and extending in a thin plate shape, and a spacer part 393 keeping a predefined interval (0.7 mm in this example) between these sheet plates 391, 392. Similarly, the second flow-path forming member 380 is made up of two sheet plates 381, 382 facing each other and extending in a thin plate shape, and a spacer part 383 keeping a predefined interval between these sheet plates 381, 382. The sheet plate 381 and the spacer part 383 are shown in FIG. 9 (in FIG. 9, the sheet plates 392, 382 on the side far from the inner case member 11 are omitted for facilitating understanding; FIG. 9 will be described later). Lateral pins 390 p and 380 p are integrally attached to an end portion of the first flow-path forming member 390 and an end portion of the second flow-path forming member 380, respectively, in a manner allowing a fluid to flow. When the cuff structure 20 including the curler 24 is attached to the main body 10, the flexible tube 39 from the pressing cuff 23 is connected via the lateral pin 390 p to the first flow-path forming member 390. The flexible tube 38 from the sensing cuff 21 is connected via the lateral pin 380 p to the second flow-path forming member 380.

The first flow-path forming member 390 and the second flow-path forming member 380 are formed by integral molding of an elastomer in this example. The thickness dimensions of the first flow-path forming member 390 and the second flow-path forming member 380 are set to 1.2 mm in this example.

FIG. 10 shows a block configuration of a control system of the sphygmomanometer 1. The main body 10 of the sphygmomanometer 1 is equipped with, in addition to the display 50 and the operation part 52 described above, as the blood-pressure measurement elements for performing a blood pressure measurement, a main CPU (central processing unit) 100 serving as a control part, a sub-CPU 101, a memory 51 serving as a storage part, an acceleration sensor 54, a communication part 59, a battery 53, a first pressure sensor 31 for detecting the pressure of the pressing cuff 23, a second pressure sensor 32 for detecting the pressure of the sensing cuff 21, the pump 30, an on-off valve 33, and a pump drive circuit 35 driving the pump 30. The main CPU 100 mainly controls the operation of the entire sphygmomanometer 1, and the sub-CPU 101 mainly controls the operation of an air system. Hereinafter, for simplicity, the main CPU 100 and the sub-CPU 101 will collectively be referred to simply as the CPU 100.

The display 50 is made up of an LCD (liquid crystal display) in this example and displays information on blood pressure measurement such as a blood pressure measurement result and other information in accordance with a control signal from the CPU 100. The display 50 is not limited to the organic EL display and may be another type of the display 50, for example, an organic EL (electro luminescence) display. The display 50 may include an LED (light emitting diode).

As described above, the operation part 52 includes the measurement switch 52A for giving an instruction for starting or stopping a blood pressure measurement, the home switch 52 b for returning the display screen of the display 50 to a predetermined home screen, and the record calling switch 52C for instructing the display 50 to display past measurement records of blood pressure, activity amount, etc. In this example, these switches 52A to 52C are made up of push switches and input operation signals to the CPU 100 in accordance with an instruction for starting or stopping a blood pressure measurement from the user. The operation part 52 is not limited to the push switches, and may be, for example, pressure-sensitive (resistive) or proximity (electrostatic-capacitive) touch-panel switches. Additionally, a microphone not shown may be included for input of an instruction for starting a blood pressure measurement through a user's voice.

The memory 51 non-transitory stores data of a program for controlling the sphygmomanometer 1, data used for controlling the sphygmomanometer 1, setting data for setting various functions of the sphygmomanometer 1, data of measurement results of blood pressure values, etc. The memory 51 is also used as a work memory etc. when a program is executed.

The CPU 100 executes various functions as the control part in accordance with a program for controlling the sphygmomanometer 1 stored in the memory 51. For example, when executing the blood-pressure measurement function, the CPU 100 provides a control of driving the pump 30 and the on-off valve 33 based on signals from the first pressure sensor 31 and the second pressure sensor 32 in accordance with the instruction for starting a blood pressure measurement from the measurement switch 52A of the operation part 52. The CPU 100 also provides a control of calculating a blood pressure value, a pulse, etc. based on a signal from the second pressure sensor 32.

The acceleration sensor 54 is made up of a three-axis acceleration sensor integrally built in the main body 10. The acceleration sensor 54 outputs to the CPU 100 an acceleration signal indicative of the accelerations of the main body 10 in three directions orthogonal to each other. In this example, the output of the acceleration sensor 54 is used for measuring an activity amount.

The communication part 59 is controlled by the CPU 100 to transmit predetermined information through a network to an external apparatus or to receive information from the external apparatus through the network and deliver the information to the CPU 100. The communication through the network may be either wireless or wired. In this embodiment, the network is the Internet; however, the present invention is not limited thereto, and the network may be another type of network such as an intra-hospital LAN (local area network) or may be a one-to-one communication using a USB cable etc. The communication part 59 may include a micro USB connector.

The battery 53 is made up of a rechargeable secondary battery in this example. The battery 53 supplies electric power to the elements mounted on the main body 10, i.e., the CPU 100, the memory 51, the acceleration sensor 54, the communication part 59, the first pressure sensor 31, the second pressure sensor 32, the pump 30, the on-off valve 33, and the pump drive circuit 35 in this example.

The pump 30 is made up of a piezoelectric pump in this example and is driven by the pump drive circuit 35 based on a control signal supplied from the CPU 100. The pump 30 is connected via the first flow-path forming member 390 and the flexible tube 39 constituting a first flow path to the pressing cuff 23 in a manner allowing a fluid to flow. The pump 30 can supply air as a pressurizing fluid to the pressing cuff 23 through the first flow-path forming member 390 and the flexible tube 39. The pump 30 is equipped with an exhaust valve (not shown) controlled to open and close in accordance with on/off of the pump 30. Specifically, when the pump 30 is turned on, the exhaust valve closes to assist enclosing air in the pressing cuff 23, and when the pump 30 is turned off, the exhaust valve opens to discharge the air in the pressing cuff 23 to the atmosphere through the flexible tube 39 and the first flow-path forming member 390. This exhaust valve has a function of a check valve so that the air to be discharged does not flow backward.

The pump 30 is connected via the second flow-path forming member 380 and the flexible tube 38 constituting a second flow path to the sensing cuff 21 in a manner allowing a fluid to flow. The on-off valve (normally open solenoid valve in this example) 33 is interposed in the second flow path (actually, between the first flow-path forming member 390 and the second flow-path forming member 380). The opening/closing (opening degree) of the on/off valve 33 is controlled based on a control signal supplied from the CPU 100. When the on-off valve 33 is in an opened state, air can be supplied and stored as pressure-transmitting fluid from the pump 30 through the second flow path to the sensing cuff 21.

The first pressure sensor 31 and the second pressure sensor 32 are each made up of a piezoresistive pressure sensor in this example. The first pressure sensor 31 detects the pressure in the pressing cuff 23 via the first flow-path forming member 390 and the flexible tube 39 constituting the first flow path. The second pressure sensor 32 detects the pressure in the sensing cuff 21 via the second flow-path forming member 380 and the flexible tube 38 constituting the second flow path.

As shown in FIG. 8 (when the inside of the main body 10 is viewed obliquely from above), the pump 30 and the first pressure sensor 31 are disposed substantially at the center of the inner case member 11 in the main body 10. The on-off valve 33 and the second pressure sensor 32 are disposed around the inner case member 11. As shown in FIG. 9 (when the inside of the main body 10 is viewed obliquely from below), the first flow-path forming member 390 is disposed on the back side of the inner case member 11 to extend over a discharge port 30 d of the pump 30, an air introducing port 31 d of the first pressure sensor 31, an inlet 33 i of the on-off valve 33. The second flow-path forming member 380 is disposed on the back side of the inner case member 11 to extend over an outlet 33 e of the on-off valve 33 and an air introducing port 32 d of the second pressure sensor 32.

The sphygmomanometer 1 is small-sized and integrally formed by mounting the blood-pressure measurement elements as described above on the main body 10. Therefore, the usability for the user is good.

(Operation of Blood Pressure Measurement)

FIG. 11 shows an operation flow when the user performs a blood-pressure measurement method of an embodiment to measure a blood pressure with the sphygmomanometer 1.

As shown in step S1 of FIG. 11, the user wears the sphygmomanometer 1 on the left wrist 90 that is a measurement site. At the time of wearing, as shown in FIG. 13A, the user first wears the cuff structure 20 on the left wrist 90 by using a right hand 99 (step S21 of FIG. 12). The cuff structure 20 is curved along the circumferential direction Y of the left wrist 90 due to the curler 24 in the natural state. Therefore, in this example, the user fits the cuff structure 20 onto the outer circumferential surface of the left wrist 90 by using the hand (the right hand 99 in this example) on the right side of the body, i.e., on the side opposite to the left side of the body to which the left wrist 90 belongs, and can thereby easily wear the cuff structure 20 on the left wrist 90. While the cuff structure 20 is worn on the left wrist 90, the cuff structure 20 grips the left wrist 90 even when the user releases the right hand 99 from the cuff structure 20, so that the cuff structure 20 (as well as the belt 2 and the main body 10) hardly drops off.

Subsequently, as shown in FIG. 135, the user uses the right hand 99 to bring the left wrist 90 and the cuff structure 20 into a state of being wrapped with the belt 2 together. Specifically, a portion leading to the tip portion 4 f of the second belt part 4 is passed through the frame-shaped body 5A of the buckle 5 of the first belt part 3, and the prong 5B of the buckle 5 is then inserted into any one of the multiple small holes 4 w, 4 w . . . of the second belt part 4. Consequently, as shown in FIG. 13C, the first belt part 3 and the second belt part 4 are fastened (step S22 of FIG. 12). As a result, the left wrist 90 is wrapped with the belt 2 extending from the main body 10, and the strap-shaped cuff structure 20 having the one end 20 f attached to the main body 10 is disposed on the inner circumferential side closer to the left wrist 90 than the belt 2.

In the sphygmomanometer 1, the cuff structure 20 can be separated from the inner circumferential surfaces 3 a, 4 a of the belt 2, and the other end 20 e on the side opposite to the one end 20 f of the cuff structure 20 is a free end. Therefore, when the first belt part 3 and the second belt part 4 are fastened, the cuff structure 20 receives an inward force from the belt 2, and the cuff structure 20 may slide or deform exactly along the outer circumferential surface of the left wrist 90. As a result, in the worn state, the cuff structure 20 and the belt 2 are brought substantially into close contact with the outer circumferential surface of the left wrist 90 in this order, i.e., a state of wrapping the left wrist 90 in a strap shape as a whole. In this way, the sphygmomanometer 1 may easily be worn on the left wrist 90.

Specifically, as shown in FIG. 14, in this worn state, the bag-shaped pressing cuff 23 extends along the circumferential direction Y of the left wrist 90 on the inner circumferential side of the curler 24 included in the cuff structure 20. The bag-shaped sensing cuff 21 included in the cuff structure 20 is disposed on the inner circumferential side relative to the pressing cuff 23 and in contact with the left wrist 90 and extends in the circumferential direction Y to cross an artery-passing portion 90 a of the left wrist 90. Furthermore, the back plate 22 included in the cuff structure 20 is interposed between the pressing cuff 23 and the sensing cuff 21 and extends along the circumferential direction Y of the left wrist 90. In FIG. 14, the main body 10 and the belt 2 are not shown. In FIG. 14, a radius 93, an ulna 94, a radial artery 91, an ulnar artery 92, and tendons 96 of the left wrist 90 are shown.

Subsequently, when the user presses the measurement switch 52A of the operation part 52 disposed on the main body 10 (step S2 of FIG. 11), the CPU 100 initializes a processing memory area (step S3 of FIG. 11). The CPU 100 turns off the pump 30 via the pump drive circuit 35, opens the exhaust valve built in the pump 30, and maintains the on-off valve 33 in the opened state to exhaust the air in the pressing cuff 23 and the sensing cuff 21. Subsequently, control is provided to adjust 0 mmHg of the first pressure sensor 31 and the second pressure sensor 32.

The CPU 100 then functions as a pressurization control part and a fluid storage control part to turn on the pump 30 via the pump drive circuit 35 (step S4 of FIG. 11), maintains the on-off valve 33 in the opened state, and starts pressurization of the pressing cuff 23 and the sensing cuff 21 (step S5 of FIG. 11). In a pressurization process, the pump 30 is driven via the pump drive circuit 35 while the pressures of the pressing cuff 23 and the sensing cuff 21 are monitored by the first pressure sensor 31 and the second pressure sensor 32, respectively. As a result, controls are provided to respectively send air to the pressing cuff 23 through the first flow path (the first flow-path forming member 390 and the flexible tube 39) and to the sensing cuff 21 through the second flow path (the second flow-path forming member 380 and the flexible tube 38).

At step S6 of FIG. 11, the CPU 100 then functions as the fluid storage control part to determine whether the pressure of the sensing cuff 21 has reached a predetermined pressure (15 mmHg in this example) or whether the drive time of the pump 30 has elapsed for a predetermined time (three seconds in this example). The reason for making this determination is to confirm whether an appropriate amount of air is stored in the sensing cuff 21. In the case of NO at step S6 of FIG. 11, the CPU 100 waits until the pressure of the sensing cuff 21 reaches a predetermined pressure or the drive time of the pump 30 elapses for a predetermined time. An amount of the pressure-transmitting fluid stored in the sensing cuff 21 considered as the “appropriate amount” will be described later.

In the case of YES at step S6 of FIG. 11, it is determined that the appropriate amount of air is stored in the sensing cuff 21. At step S7 of FIG. 11, the CPU 100 then functions as the pressurization control part, brings the on-off valve 33 into the closed state, and continues a control of supplying air from the pump 30 through the first flow path to the pressing cuff 23. As a result, the pressing cuff 23 is inflated, and a pressure is gradually applied to compress the left wrist 90. At this point, the back plate 22 transmits the pressing force from the pressing cuff 23 to the sensing cuff 21. The sensing cuff 21 compresses the left wrist 90 (including the artery-passing portion 90 a). In this pressurization process, to calculate a blood pressure value, the CPU 100 monitors a pressure Pc of the sensing cuff 21, i.e., the pressure of the artery-passing portion 90 a of the left wrist 90, by the second pressure sensor 32, to acquire a pulse wave signal Pm as a variation component. FIG. 16 exemplarily shows the pressure Pc of the sensing cuff 21 and a waveform of the pulse wave signal Pm acquired in this pressurization process.

FIGS. 15A and 15B schematically shows a cross section along the longitudinal direction of the left wrist 90 (corresponding to the width direction X of the cuff) in a pressurized state when an appropriate amount of air is stored in the sensing cuff 21 and the on/off valve 33 is closed. FIG. 15A shows a cross section (corresponding to a cross section taken along a line XVA-XVA of FIG. 14 as viewed in a direction of arrows) of a portion through which the tendon 96 of the left wrist 90 passes. On the other hand, FIG. 15B shows a cross section (corresponding to a cross section taken along a line XVB-XVB of FIG. 14 as viewed in a direction of arrows) of a portion through which the radial artery 91 of the left wrist 90 passes. As shown in FIG. 15B, a portion of the left wrist 90 having the radial artery 91 passing therethrough is relatively soft, so that a gap 21 w with air present therein remains between the first sheet 21A and the second sheet 21B of the sensing cuff 21. Therefore, the portion of the sensing cuff 21 facing the radial artery 91 can reflect the pressure of the artery-passing portion 90 a of the left wrist 90. On the other hand, as shown in FIG. 15A, a portion of the left wrist 90 having the tendon 96 passing therethrough is relatively hard, so that the first sheet 21A and the second sheet 21B are in contact with each other in a portion corresponding to substantially the center in the width direction X of the sensing cuff 21. However, the sensing cuff 21 is provided with the sags 21 r, 21 r extending along the longitudinal direction Y (corresponding to the circumferential direction of the left wrist 90) as described above at positions leading to the edge portions 21 m, 21 m on both sides in the width direction X, so that gaps 21 w′, 21 w′ with air present therein remain along the longitudinal direction Y. Consequently, the air stored in the sensing cuff 21 can flow along the longitudinal direction Y of the sensing cuff 21 through the gaps 21 w′, 21 w′. Therefore, the sensing cuff 21 can successfully transmit the pressure applied to the artery-passing portion 90 a of the left wrist 90 as the pressure of air (pressure-transmitting fluid) to the second pressure sensor 32 in the main body 10.

At step S8 of FIG. 11, the CPU 100 then functions as a blood-pressure calculating part and attempts to calculate a blood pressure value (systolic blood pressure SBP and diastolic blood pressure DBP) based on the pulse wave signal Pm acquired at this point by applying a known algorithm with the oscillometric method.

At this point, when the blood pressure value cannot yet be calculated because of insufficient data (NO at step S9), the processes of steps S7 to S9 are repeated as long as the cuff pressure process has not reached an upper limit pressure (predetermined for safety as, e.g., 300 mmHg).

When the blood pressure value is calculated in this way (YES at step S9), the CPU 100 stops the pump 30 (step S10) and opens the on-off valve 33 (step S11) to provide control of exhausting the air inside the pressure cuff 23 and the sensing cuff 21. Lastly, the measurement result of the blood pressure value is displayed on the display 50 (step S12).

The blood pressure calculation may be performed in a depressurization process rather than the pressurization process of the pressing cuff 23.

As described above, in the sphygmomanometer 1, air is stored in the sensing cuff 21 each time the blood pressure is measured, and the second pressure sensor 32 detects the pressure Pc of the sensing cuff 21, i.e., the pressure of the artery-passing portion 90 a of the left wrist 90 itself, separately from the pressing cuff 23. Therefore, even if the pressing cuff 23 is largely inflated in the thickness direction and causes a compression loss at the time of pressurization as a result of setting a small dimension (e.g., about 25 mm) in the width direction X for the belt 2 and the cuff structure 20 (collectively referred to simply as a “cuff” as appropriate), the blood pressure can accurately be measured. In the worn state, the sensing cuff 21 extends in the circumferential direction Y to cross the artery-passing portion 90 a of the left wrist 90. Therefore, even if the user actually wears the sphygmomanometer 1 on the left wrist 90 and the cuff is positionally displaced to some extent along with the main body 10 in the circumferential direction Y of the left wrist 90, the sensing cuff 21 does not fall outside the arterial passing portion 90 a of the left wrist 90. Therefore, the blood pressure measurement value can be prevented from varying relative to the actual blood pressure, and consequently, the blood pressure can accurately be measured.

In the above example, air is stored as the pressure-transmitting fluid in the sensing cuff 21 each time the blood pressure is measured, and the air is exhausted after the measurement is completed; however, the present invention is not limited thereto. At a manufacturing stage of the sphygmomanometer 1, a pressure-transmitting fluid may be stored and sealed in the sensing cuff 21.

(Appropriate Amount of Pressure-Transmitting Fluid Stored in Sensing Cuff)

FIG. 17 shows a blood-pressure measurement error (average value) when water is used as the pressure-transmitting fluid stored in the sensing cuff 21 and an amount of water stored in the sensing cuff 21 is variably set. The blood-pressure measurement error means a difference acquired by subtracting a blood pressure value (systolic blood pressure SBP) measured by a standard (correct) sphygmomanometer (this is called “reference blood pressure value”) from a blood pressure value (systolic blood pressure SBP) measured by the sphygmomanometer 1 for a certain user (subject). This is represented as follows:

(blood-pressure measurement error)=(blood pressure value measured by the sphygmomanometer 1)−(reference blood pressure value). As can be seen from FIG. 17, when the amount of water stored in the sensing cuff 21 is within a range wa of 0.26 ml±0.05 ml, the blood-pressure measurement error is within ±5 mmHg, so that the amount is considered as an appropriate amount.

In FIG. 17, when the amount of water exceeds the appropriate amount range wa, the blood-pressure measurement error becomes larger on the positive side. Possible reasons are that since water intervenes also on a hard portion such as the tendons 96 in the cross section shown in FIG. 14, the internal pressure of the sensing cuff 21 rises when being compressed, and that since portions having the radial artery 91 and the ulnar artery 92 passing therethrough are relatively soft, the water present more than necessary in these portions expands the sensing cuff 21 and raises the internal pressure of the sensing cuff 21 due to tension of the expansion. In FIG. 17, when the amount of water falls below the appropriate range wa, the blood-pressure measurement error becomes larger on the negative side. A possible reason is that the amount of water becomes too small around the arteries.

As a result, it is considered in this example that an appropriate amount of the pressure-transmitting fluid stored in the sensing cuff 21 is within the range wa of 0.26 ml±0.05 ml. At step S6 of FIG. 11 descried above, a criterion for determination on whether the pressure of the sensing cuff 21 has reached a predetermined pressure (15 mmHg in this example) or whether the drive time of the pump 30 has elapsed for a predetermined time (three seconds in this example) is set to satisfy the condition that the amount of air stored as the pressure-transmitting fluid in the sensing cuff 21 is within the range wa of 0.26 ml±0.05 ml.

Obviously, the appropriate amount of the pressure-transmitting fluid stored in the sensing cuff 21 depends on the size etc. of the sensing cuff 21.

(Verification Result)

A scatter diagram of FIG. 18 shows a relationship between the reference blood pressure value and the blood-pressure measurement error when the amount of the pressure-transmitting fluid stored in the sensing cuff 21 is variably set to “small water amount”=0.16 ml, “appropriate amount”=0.3 ml, “large water amount”=0.8 ml for multiple users (in this example, measurement is performed three times for each of five subjects with the systolic blood pressure SBP of 97 mmHg to 149 mmHg). When the amount of water is the “appropriate amount”, the blood-pressure measurement error is reduced for the multiple users as indicated by square marks in the figure. On the other hand, in the case of the “large water amount”, the blood-pressure measurement error becomes larger on the positive side for the multiple users as indicated by cross marks in the figure. In the case of the “small water amount”, the blood-pressure measurement error becomes larger on the negative side for the multiple users as indicated by diamond marks in the figure.

This verification result can be considered as giving confirmation to the fact that the sphygmomanometer 1 of the present invention can accurately measure the blood pressure even when the blood pressure is measured by using the bag-shaped sensing cuff on the measurement site that is the wrist where the tendons 96, the radius 93, and the ulna 94 exist.

Particularly, when multiple users each actually wear the sphygmomanometer 1 on the left wrist 90 and measure the blood pressure, the area of the soft portion having the two arteries, i.e., the radial artery 91 and the ulnar artery 92, is different depending on a user. In the verification result of FIG. 18, when the amount of water is appropriate, the blood-pressure measurement errors are suppressed for the multiple users. Therefore, the verification result can be considered as giving confirmation to the fact that this sphygmomanometer 1 can accurately measure the blood pressure even when the area of the soft portion having the two arteries, i.e., the radial artery 91 and the ulnar artery 92, is different.

(Dimensions in Width Direction of Back Plate and Sensing Cuff)

FIG. 19 is a schematic view showing a relationship of dimensions in the width direction X of the curler 24, the pressing cuff 23, the back plate 22, and the sensing cuff 21. In FIG. 19, the center positions in the width direction X of the curler 24, the pressing cuff 23, the back plate 22, and the sensing cuff 21 are aligned with the X-coordinate origin. FIG. 20A is a diagram showing results of simulations of pressure distribution on a skin surface (the left wrist 90) and pressure distribution around blood vessels when a pressure of 300 mmHg is applied to the back plate 22 by the pressing cuff. FIG. 20B is a view showing results of simulations of pressure distribution on a skin surface and pressure distribution around blood vessels when a pressure of 300 mmHg is applied to the skin surface (the left wrist 90) by the pressing cuff. X coordinate positions of FIGS. 20A and 20B correspond to X coordinate positions of FIG. 19.

As shown in FIG. 20B, when the measurement site is pressed by the pressing cuff 23 without disposing the back plate 22, pressures are substantially identical at a skin surface position and a blood vessel position and are high in a central portion while decreasing toward edge portions in the width direction X. However, as shown in FIG. 20A, when the back plate 22 is disposed and the measurement site is pressed by the pressing cuff 23 and the back plate 22, the pressures at the skin surface position and the blood vessel position are identical and uniform in the central portion. However, the pressure at the skin surface position is extremely high near edge portions 22 f in the width direction X as compared to the pressure at the blood vessel position, causing a deviation from the pressure at the blood vessel position. A possible reason is that since the back plate 22 used in the simulation is a plate-shaped member as shown in FIG. 19 and has a shape with edges 22 c at the edge portions 22 f in the width direction X, stress concentration occurs due to the edges 22 c. As described above, in the case of pressing via the back plate 22, although a range of uniform pressure becomes wider than in the case of the pressing cuff 23 alone, the stress concentration causes a pressure deviation between the skin surface position and the blood vessel position. Therefore, when the dimension in the width direction X of the sensing cuff 21 is the same as the dimension in the width direction X of the back plate 22, the deviation occurs between the skin surface position and the blood vessel position in the pressure in the width direction X of the sensing cuff 21 to the measurement site, causing an error in the measured blood pressure value.

Therefore, in this embodiment, as shown also in FIG. 3B, the respective dimensions in the width direction X of the curler 24, the pressing cuff 23, the back plate 22, and the sensing cuff 21 are set to W1=28 mm, W2=25 mm, W3=23 mm, and W4=15 mm. Therefore, in this embodiment, the dimension in the width direction X of the back plate 22 is made larger than the dimension in the width direction X of the sensing cuff 21. This configuration makes the pressures identical at the skin surface position and the blood vessel position in FIG. 20B even though the back plate 22 has a shape with the edges 22 c, and the sensing cuff 21 can be pressed in a region with uniform pressure. Consequently, no deviation occurs in pressure between the skin surface position and the blood vessel position at the measurement site of the sensing cuff 21, and the pressing force to the measurement site becomes uniform, so that an error can be prevented from occurring in the measured blood pressure value. Therefore, the sphygmomanometer 1 can accurately measure the blood pressure.

(Structure of Edge Portion in Width Direction of Back Plate)

FIG. 21 is a schematic view showing the back plate 22 in which a surface 22 g facing the measurement site in the edge portions 22 f on both sides in the width direction X is curved in a direction away from the measurement site toward tips. FIG. 22 is a schematic view showing the back plate 22 in which the surface 22 g facing the measurement site in the edge portions 22 f on both sides in the width direction X is curved in a direction away from the measurement site. In FIGS. 21 and 22, the center positions in the width direction X of the back plate 22 and the sensing cuff 21 are aligned with the X-coordinate origin. FIG. 23 is a diagram showing results of simulations of pressure distribution on a skin surface and pressure distribution around blood vessels when a pressure of 300 mmHg is applied to the back plate 22 of FIG. 21 by the pressing cuff 23. FIG. 24 is a diagram showing results of simulations of pressure distribution on a skin surface and pressure distribution around blood vessels when a pressure of 300 mmHg is applied to the back plate 22 of FIG. 22 by the pressing cuff 23.

It can be seen that when the surface 22 g of the back plate 22 facing the measurement site in the edge portions 22 f on both sides in the width direction X is curved in the direction away from the measurement site toward the tips as shown in FIG. 21, the pressures at the skin surface position and the blood vessel position of the measurement site are substantially identical as shown in FIG. 23. On the other hand, it can be seen that when the surface 22 g of the back plate 22 facing the measurement site in the edge portions 22 f on both sides in the width direction X is curved in the direction away from the measurement site to form the edges 22 c between a bottom surface 22 e and the surface 22 g as shown in FIG. 22, the pressure at the skin surface position of the measurement site is higher than the pressing force at the blood vessel position near the edges 22 c as shown in FIG. 24. A possible reason is that since the edges 22 c are formed in the back plate 22 shown in FIG. 22 although the surface 22 g is curved in the direction away from the measurement site, stress concentration occurs due to the edges 22 c.

Therefore, it is found that, to eliminate the deviation in the pressure of the sensing cuff 21 to the measurement site at the skin surface position and the blood vessel position of the measurement site to make the pressure more uniform, preferably, in addition to making the dimension in the width direction X of the back plate 22 larger than the dimension in the width direction X of the sensing cuff 21 as described above, the surface 22 g of the back plate 22 facing the measurement site in the edge portions 22 f on both sides in the width direction X is curved in the direction away from the measurement site toward the tips. This configuration eliminates the deviation in the pressure of the sensing cuff 21 to the measurement site at the skin surface position and the blood vessel position of the measurement site to make the pressure more uniform and reduces the error in the measured blood pressure value, so that the blood pressure can accurately be measured. To curve the surface 22 g, the surface 22 g may be processed into a rounded shape or may be processed into a tapered shape. In other words, by gradually thinning the edge portions 22 f on both sides of the back plate 22 toward the tips, the influence of the stress concentration due to the edges can be reduced.

FIG. 25 is a schematic view when the width-direction dimensions are made equal between the sensing cuff 21 and the back plate 22 in which the surface 22 g facing the measurement site in the edge portions 22 f on both sides in the width direction X is curved in the direction away from the measurement site toward the tips. In the case of this configuration, the deviation occurs in the pressure of the sensing cuff 21 to the measurement site at the skin surface position and the blood vessel position of the measurement site as compared to when the dimension in the width direction X of the back plate 22 is made larger than the dimension in the width direction X of the sensing cuff 21 as shown in FIG. 19, and the pressure uniformity is impaired. This is because the pressure in the width direction X of the back plate 22 changes due to the curved edge portions 22 f as compared to when the bottom surface 22 e of the back plate 22 is entirely flat in the width direction X of the sensing cuff 21. However, the back plate 22 shown in FIG. 25 has no edge between the curved edge portions 22 f and the bottom surface 22 e, no stress concentration occurs at the measurement site, and the error in the measured blood pressure value is not so large. Therefore, in the case that the surface of the back plate 22 in the edge portions 22 f on both sides in the width direction X is curved in the direction away from the measurement site toward the tips as shown in FIG. 25, the blood pressure can accurately be measured even when the width-direction dimension of the back plate 22 is the same as the width-direction dimension of the sensing cuff 21.

In the embodiment described above, the multiple grooves 22 d 1, 22 d 2 having V-shaped or U-shaped cross sections and extending in the width direction X are disposed on the inner circumferential surface 22 a and the outer circumferential surface 22 b of the back plate 22 and parallelly separated from each other in the longitudinal direction Y. However, the present invention is not limited thereto. The back plate may be made up of a set of multiple small pieces separated from each other in the longitudinal direction Y such that the back plate may be curved along the circumferential direction of the measurement site (the longitudinal direction Y) as a whole, and the set of multiple small pieces may be arranged over a range exceeding the length of the sensing cuff 21 in the circumferential direction of the measurement site (longitudinal direction Y). Even in this case, substantially the same effect as the back plate 22 described above can be produced.

In the embodiment described above, the left wrist 90 is the measurement site on which the sphygmomanometer is worn. However, the present invention is not limited thereto. The sphygmomanometer of the present invention may be configured to be optically symmetric to the sphygmomanometer 1 shown in FIGS. 1 and 2 and may be worn on the right wrist. The measurement site may be a site other than the wrist, such as an upper arm and a lower limb.

The embodiment described above is configured such that the main body 10 and the belt 2 are formed separately from each other and that the belt 2 is attached to the main body 10. However, the present invention is not limited thereto. The main body 10 and the belt 2 may integrally be molded.

In the embodiment described above, the first belt part 3 and the second belt part 4 of the belt 2 are fastened or released by the buckle 5. However, the present invention is not limited thereto. For example, the first belt part 3 and the second belt part 4 may be coupled to each other via an openable/closable triple-folding buckle.

In the embodiment described above, the cuff structure 20 includes the curler 24 in the described example. However, the present invention is not limited thereto, and the curler 24 may not be included. In this case, the belt 2 may be formed of one strap-shaped body; the pressing cuff 23 may be disposed along the inner circumferential surface of the strap-shaped body; the back plate 22 may be disposed along the inner circumferential surface of the pressing cuff 23; and the sensing cuff 21 may be disposed along the inner circumferential surface of the back plate 22. In this case, the belt 2 described above and the pressing cuff 23 function as pressing members capable of generating a pressing force toward the wrist, and these pressing members press the back plate 22 toward the wrist that is the measurement site, and the wrist is compressed via the sensing cuff 21 interposed between the back plate 22 and the wrist. Regarding the belt 2, for example, the back lid 10C of the main body 10 may include an openable/closable triple-folding buckle, and the end portions of the belt 2 may be coupled to the triple-folding buckle.

In the embodiment described above, the pump 30 is driven until the pressure of the sensing cuff 21 reaches 15 mmHg, or the drive time of the pump 30 is set to three seconds, in the pressurization process of the sensing cuff 21 shown in step S6 of FIG. 11. However, the present invention is not limited to this example, and the pump 30 may be driven until the pressure of the sensing cuff 21 reaches, for example, 5 mmHg, and after the fluid is filled in the sensing cuff 21, an amount of the fluid in the sensing cuff 21 may gradually be optimized. Alternatively, after air is first filled in the sensing cuff 21 by the pump 30 until reaching a relatively high pressure, for example, 30 mmHg, the pump 30 may be stopped and the exhaust valve may be opened to reduce the pressure of the sensing cuff 21 to a relatively low pressure, for example, 15 mmHg, and the exhaust valve may be closed to optimize the fluid volume in the sensing cuff 21. In this case, the exhaust valve may be disposed separately from the pump 30, and a valve drive circuit driving the exhaust valve may be disposed to be controllable by the CPU 100.

In the embodiment described above, the sensing cuff 21 is in direct contact with the left wrist 90 that is the measurement site in the described example; however, the present invention is not limited thereto. The sensing cuff 21 may be in indirect contact with the left wrist 90 via another member (e.g., a cover member).

In the embodiment described above, the belt 2, the curler 24, and the pressing cuff 23 are described as examples of the pressing member; however, the present invention is not limited thereto, and the pressing member may mechanically extend in the thickness direction.

In the embodiment described above, the pump 30 is included in the main body 10 in the described example; however, the present invention is not limited thereto, and a cuff including the belt 2 and the cuff structure 20 and a main body placed on a table may be included, and the pump may be included in this main body. In this case, the cuff and the main body may be connected via an elongated tube, and a fluid may be supplied from the main body to the cuff.

In the embodiment described above, the CPU 100 mounted on the sphygmomanometer 1 functions as the fluid storage control part, the pressurization control part, and the blood-pressure calculating part to perform the blood pressure measurement (the operation flow of FIG. 11). However, the present invention is not limited thereto. For example, a substantial computer device such as a smartphone disposed outside the sphygmomanometer 1 may function as the fluid storage control part, the pressurization control part, and the blood-pressure calculating part to cause the sphygmomanometer 1 to perform the blood pressure measurement (the operation flow of FIG. 11) via a network 900.

As described above, a sphygmomanometer of the present disclosure is a sphygmomanometer comprising:

a bag-shaped sensing cuff to be worn to wrap a measurement site;

a back plate disposed on the sensing cuff along a surface opposite to the measurement site;

a pressing member for pressing the back plate toward the measurement site; and

a blood-pressure calculating part calculating a blood pressure based on a pressure of a fluid stored in the sensing cuff, wherein

regarding a longitudinal direction perpendicular to a circumferential direction of the measurement site to be wrapped by the sensing cuff, a surface facing the measurement site in edge potions on both sides in a width direction along the longitudinal direction of the back plate is curved in a direction away from the measurement site toward tips with the edge portions on both sides respectively gradually becoming thinner toward the tips.

As used herein, the term “measurement site” refers to a site through which an artery passes. The measurement site may be, for example, an upper limb such as a wrist and an upper arm, or a lower limb such as an ankle and a thigh.

The sphygmomanometer according to the present disclosure has the sensing cuff worn to wrap the measurement site, the sensing cuff has the back plate disposed on the sensing cuff along a surface opposite to the measurement site, and the back plate is pressed by the pressing member toward the measurement site. Consequently, the sensing cuff compresses the measurement site. When the pressing member is pressurized or depressurized, the blood pressure is calculated by the blood-pressure calculating part in this process based on the pressure of the fluid stored in the sensing cuff (the oscillometric method).

In this sphygmomanometer, the sensing cuff detects the pressure itself applied to an artery-passing portion of the measurement site. In this case, a surface of the back plate facing the measurement site in edge potions on both sides in a width direction along the longitudinal direction perpendicular to the circumferential direction of the measurement site is curved in a direction away from the measurement site toward tips with the edge portions on both sides respectively gradually becoming thinner toward the tips. Therefore, this curved surface presses the measurement site or the back plate, so that stress concentration due to the edge portions in the width direction of the back plate is reduced or not occurred. Consequently, the sensing cuff is pressed by a pressing force in a range without significant variations due to stress concentration in the width direction, so that a detection error of the blood pressure value is reduced. Therefore, the blood pressure can accurately be measured.

In the sphygmomanometer of an embodiment,

a dimension of the back plate in the width direction is larger than a dimension of the sensing cuff in the width direction.

In the sphygmomanometer of this embodiment, since a dimension of the back plate in the width direction is larger than a dimension of the sensing cuff in the width direction, variations in the pressing force from the edge portions in the width direction of the back plate do not affect the sensing cuff. In other words, the sensing cuff is pressed by the pressing force in a range without significant variations in the width direction, so that a detection error of the blood pressure value is reduced. Therefore, the blood pressure can accurately be measured.

In the sphygmomanometer of an embodiment,

the back plate extends in a strap shape beyond the length of the sensing cuff in the circumferential direction, and

the back plate includes a plurality of grooves having V-shaped or U-shaped cross sections, extending in the width direction of the back plate, and parallelly separated from each other in the longitudinal direction of the back plate, which allows the back plate to curve along the circumferential direction.

In the sphygmomanometer of the embodiment, the back plate extends in a strap shape beyond the length of the sensing cuff in the circumferential direction. Therefore, the back plate can transmit the pressing force from the pressing cuff to an entire area in the longitudinal direction of the sensing cuff (corresponding to the circumferential direction). The back plate includes a plurality of grooves having V-shaped or U-shaped cross sections, extending in the width direction of the back plate, and parallelly separated from each other in the longitudinal direction of the back plate (corresponding to the circumferential direction), which allows the back plate to curve along the circumferential direction. Therefore, when the user brings the measurement site and the cuff structure into a state of being wrapped with the belt together at the time of wearing (a second step of wearing), the back plate does not prevent the cuff structure from curving along the circumferential direction.

In the sphygmomanometer of an embodiment,

the backplate is made up of a set of multiple small pieces separated from each other in the longitudinal direction, which allows the back plate to curve along the circumferential direction as a whole, and

the set of multiple small pieces is arranged over a range exceeding the length of the sensing cuff in the circumferential direction.

In the sphygmomanometer of the embodiment, the backplate is made up of a set of multiple small pieces separated from each other in the longitudinal direction, which allows the back plate to curve along the circumferential direction as a whole. Therefore, when the user brings the measurement site and the cuff structure into a state of being wrapped with the belt together at the time of wearing (the second step of wearing), the back plate does not prevent the cuff structure from curving along the circumferential direction. The set of multiple small pieces is arranged over a range exceeding the length of the sensing cuff in the circumferential direction. Therefore, the back plate can transmit the pressing force from the pressing cuff to a substantially entire area in the longitudinal direction of the sensing cuff (corresponding to the circumferential direction).

In the sphygmomanometer of an embodiment,

the sensing cuff is formed into a bag shape enabling storage of a pressure-transmitting fluid and extends in the circumferential direction to cross an artery-passing portion of the measurement site, and

the pressing member includes

a belt to be worn to wrap the measurement site in the circumferential direction, and

a bag-shaped pressing cuff disposed to face an inner circumferential surface of the belt and extending along the circumferential direction to receive a supply of a pressurizing fluid and compress the measurement site.

The pressurizing and pressure-transmitting “fluid” is typically air or may be another gas or liquid. The “pressure-transmitting fluid” may be stored in the sensing cuff at a manufacturing stage of the sphygmomanometer or may be stored in the sensing cuff and discharged from the sensing cuff each time a blood pressure is measured.

The “inner circumferential surface” of the belt refers to the surface on the inner circumferential side in the worn state in which the measurement site is wrapped.

The sphygmomanometer is worn on the measurement site with the belt wrapping the measurement site in the circumferential direction and with the pressing cuff, the back plate, and the sensing cuff arranged in this order on the inner circumferential side closer to the measurement site than the belt. In this worn state, the pressing cuff extends along the circumferential direction. The sensing cuff is disposed on the inner circumferential side relative to the pressing cuff and in contact with the measurement site and extends in the circumferential direction to cross the artery-passing portion of the measurement site. Furthermore, the back plate is interposed between the pressing cuff and the sensing cuff and extends along the circumferential direction. Therefore, a cuff of the sphygmomanometer can be formed into a strap shape as a whole, and the sphygmomanometer with good usability for the user can be provided.

As used herein, “being in contact” includes not only direct contact but also indirect contact via another member (e.g., a cover member).

The belt is desirably made of a material flexible in the thickness direction of this belt and substantially inelastic in the longitudinal direction of this belt (corresponding to the circumferential direction). As a result, the belt can easily wrap and bind the outer circumferential side described above at the time of wearing and can assist compression of the wrist at the time of blood pressure measurement.

The sphygmomanometer of an embodiment comprises

a main body equipped with a pump, and

the belt extends from the main body.

As used herein, a “belt” “extending from the main body” means that the main body and the belt may integrally be molded or that the main body and the belt may be formed separately from each other before attaching the belt to the main body. Regarding the belt itself, a first belt part extending from the main body to one side in one direction and the second belt part extending from the main body to the other side in opposite direction may be fastened or released by a buckle or may be coupled by an openable/closable buckle.

This sphygmomanometer has the pump mounted on the main body and can easily be worn on the wrist by the belt extending from the main body. Therefore, the sphygmomanometer can be small-sized and integrally formed, and the sphygmomanometer can be carried, so that the sphygmomanometer with good usability for the user can be provided.

In the sphygmomanometer of an embodiment,

the pressing cuff, the back plate, and the sensing cuff constitute a cuff structure having a strap shape and one end attached to the main body, and

the cuff structure further includes a curler for keeping a shape of the cuff structure in a natural state curved along the circumferential direction along an outer circumferential surface of the pressing cuff.

As used herein, the “curler” refers to a member typically made up of a resin plate having certain degrees of flexibility and hardness and having a shape curved along the circumferential direction surrounding the measurement site in the natural state.

The sphygmomanometer of the embodiment can easily be worn on the wrist. Specifically, at the time of wearing, first, the user wears the cuff structure on the measurement site (e.g., the left wrist) (a first step of wearing). Since the cuff structure is curved along the circumferential direction due to the curler in the natural state, the user fits the cuff structure onto an outer circumferential surface of the measurement site by using the hand (the right hand in this example) on the side opposite to the side of the body to which the measurement site (the left wrist in this example) belongs, and can thereby easily wear the cuff structure on the measurement site. While the cuff structure is worn on the measurement site, the cuff structure grips the measurement site even when the user releases the hand (the right hand in this example) from the cuff structure, so that the cuff structure (as well as the belt and the main body) hardly drops off. Subsequently, the user uses the hand (the right hand in this example) to bring the measurement site and the cuff structure into a state of being wrapped with the belt together (the second step of wearing). In this way, the sphygmomanometer of the embodiment may easily be worn on the measurement site.

Since the cuff structure is not attached to the belt, the dimension in the longitudinal direction of the cuff structure (corresponding to the circumferential direction) can be set to an optimal dimension independently of the belt.

In the sphygmomanometer of an embodiment, a root portion on the main body side of the curler forming the one end of the cuff structure is sandwiched between a member disposed in the main body and a back lid of the main body, so that the one end of the cuff structure is attached to the main body.

In the sphygmomanometer of the embodiment, a root portion on the main body side of the curler forming the one end of the cuff structure is sandwiched between a member disposed in the main body and a back lid of the main body. As a result, the one end of the cuff structure is attached to the main body. Therefore, the one end of the cuff structure is reliably held by the main body. At the time of maintenance service, the cuff structure can be replaced for the main body independently of the belt by opening the back lid of the main body.

If the main body and the belt are formed separately from each other and the belt is configured to be attached to the main body, the belt can be replaced for the main body independently of the cuff structure at the time of maintenance service.

In the sphygmomanometer of an embodiment, the other end of the cuff structure on the side opposite to the one end is a free end.

In the sphygmomanometer of the embodiment, the other end of the cuff structure on the side opposite to the one end is a free end, and therefore, when the user brings the measurement site and the cuff structure into a state of being wrapped with the belt together at the time of wearing (the second step of wearing), the cuff structure receives an inward force from the belt, and the cuff structure may slide or deform exactly along the outer circumferential surface of the measurement site. As a result, in the worn state, the cuff structure and the belt are brought substantially into close contact with the outer circumferential surface of the measurement site in this order. Consequently, the blood pressure can accurately be measured.

The sphygmomanometer of an embodiment comprises

a pressurization control part providing a control of compressing the measurement site by the pressing member via the sensing cuff, and

a fluid storage control part providing a control of supplying and storing the pressure-transmitting fluid into the sensing cuff in a worn state in which the pressing member and the sensing cuff are worn on the measurement site,

the main body is equipped with

a first flow path connecting the pump and the pressing cuff to allow a fluid to flow therebetween, and

a second flow path connecting the pump or the first flow path and the sensing cuff to allow a fluid to flow therebetween and having an on-off valve interposed therein,

in the worn state, the fluid storage control part brings the on-off valve into an opened state and supplies and stores the pressure-transmitting fluid from the pump or the first flow path through the second flow path into the sensing cuff, and

after the pressure-transmitting fluid is stored in the sensing cuff, the pressurization control part brings the on-off valve into a closed state and supplies the pressurizing fluid from the pump through the first flow path to the pressing cuff to compress the measurement site.

In the sphygmomanometer of the embodiment, the pressure-transmitting fluid can be supplied and stored into the sensing cuff with a simple configuration. Additionally, while the pressure-transmitting fluid is stored and enclosed in the sensing cuff, the pressurizing fluid can be supplied to the pressing cuff for pressurization.

In the sphygmomanometer of an embodiment,

the main body is equipped with the pressurization control part, the fluid storage control part, and the blood-pressure calculating part.

The sphygmomanometer of the embodiment may be small-sized and integrally formed. Therefore, the usability for the user is good.

In another aspect, the present disclosure provides a blood-pressure measurement method of measuring a blood pressure of a measurement site, including

a bag-shaped sensing cuff to be worn to wrap the measurement site,

a back plate disposed on the sensing cuff along a surface opposite to the measurement site and including, regarding a longitudinal direction perpendicular to a circumferential direction of the measurement site to be wrapped by the sensing cuff, a surface facing the measurement site in edge potions on both sides in a width direction along the longitudinal direction and curved in a direction away from the measurement site toward tips with the edge portions on both sides respectively gradually becoming thinner toward the tips, and

a pressing member for pressing the back plate toward the measurement site, wherein

the back plate is pressed toward the measurement site by the pressing member, and wherein

the blood pressure is calculated based on a pressure of the fluid stored in the sensing cuff.

According to the blood-pressure measurement method of the present disclosure, at the time of blood pressure measurement, the sensing cuff is worn to wrap the measurement site, the sensing cuff has the back plate disposed on the sensing cuff along a surface opposite to the measurement site, and the back plate is pressed by the pressing member toward the measurement site. Consequently, the sensing cuff compresses the measurement site. When the pressing member is pressurized or depressurized, the blood pressure is calculated by the blood-pressure calculating part in this process based on the pressure of the fluid stored in the sensing cuff (the oscillometric method).

In this method, the sensing cuff detects the pressure itself applied to an artery-passing portion of the measurement site. In this case, a surface of the back plate facing the measurement site in edge potions on both sides in a width direction along the longitudinal direction perpendicular to the circumferential direction of the measurement site is curved in a direction away from the measurement site toward tips with the edge portions on both sides respectively gradually becoming thinner toward the tips. Therefore, this curved surface presses the measurement site or the back plate, so that stress concentration due to the edge portions in the width direction of the back plate is reduced or not occurred. Consequently, the sensing cuff is pressed by a pressing force in a range without significant variations due to stress concentration in the width direction, so that a detection error of the blood pressure value is reduced. Therefore, the blood pressure can accurately be measured.

In another aspect, a device of the present disclosure is a device comprising: a blood-pressure measurement element, wherein

the blood-pressure measurement element includes

a bag-shaped sensing cuff to be worn to wrap a measurement site;

a back plate disposed on the sensing cuff along a surface opposite to the measurement site;

a pressing member for pressing the back plate toward the measurement site; and

a blood-pressure calculating part calculating a blood pressure based on a pressure of a fluid stored in the sensing cuff, wherein

regarding a longitudinal direction perpendicular to a circumferential direction of the measurement site to be wrapped by the sensing cuff, a surface facing the measurement site in edge potions on both sides in a width direction along the longitudinal direction of the back plate is curved in a direction away from the measurement site toward tips with the edge portions on both sides respectively gradually becoming thinner toward the tips.

The “device” of the present invention broadly includes devices having a blood-pressure measurement function and may be configured as a watch-type wearable device such as a smart watch, for example.

According to the device of the present disclosure, the sensing cuff is pressed by the pressing force in a range without significant variations due to stress concentration in the width direction, so that a detection error of the blood pressure value is reduced. Therefore, the blood pressure can accurately be measured.

As is apparent from the above, the sphygmomanometer, the blood-pressure measurement method, and the device of the present disclosure can make the pressing force of the sensing cuff to the measurement site uniform, so that the error of the blood pressure value is reduced. Therefore, a blood pressure measurement value can be prevented from varying relative to an actual blood pressure, and the blood pressure can accurately be measured.

The embodiments described above are illustrative, and various modifications can be made without departing from the scope of the present invention. Although the plurality of embodiments described above can be implemented independently of each other, the embodiments can be combined with each other. Although various features in different embodiments can be achieved independently of each other, features in different embodiments can be combined with each other. 

1. A sphygmomanometer comprising: a bag-shaped sensing cuff to be worn to wrap a measurement site; a back plate disposed on the sensing cuff along a surface opposite to the measurement site; a pressing member for pressing the back plate toward the measurement site; and a blood-pressure calculating part calculating a blood pressure based on a pressure of a fluid stored in the sensing cuff, wherein regarding a longitudinal direction perpendicular to a circumferential direction of the measurement site to be wrapped by the sensing cuff, a surface facing the measurement site in edge potions on both sides in a width direction along the longitudinal direction of the back plate is curved in a direction away from the measurement site toward tips with the edge portions on both sides respectively gradually becoming thinner toward the tips.
 2. The sphygmomanometer according to claim 1, wherein a dimension of the back plate in the width direction is larger than a dimension of the sensing cuff in the width direction.
 3. The sphygmomanometer according to claim 1, wherein the back plate extends in a strap shape beyond the length of the sensing cuff in the circumferential direction, and wherein the back plate includes a plurality of grooves having V-shaped or U-shaped cross sections, extending in the width direction of the back plate, and parallelly separated from each other in the longitudinal direction of the back plate, which allows the back plate to curve along the circumferential direction.
 4. The sphygmomanometer according to claim 1, wherein the backplate is made up of a set of multiple small pieces separated from each other in the longitudinal direction, which allows the back plate to curve along the circumferential direction as a whole, and wherein the set of multiple small pieces is arranged over a range exceeding the length of the sensing cuff in the circumferential direction.
 5. The sphygmomanometer according to claim 1, wherein the sensing cuff is formed into a bag shape enabling storage of a pressure-transmitting fluid and extends in the circumferential direction to cross an artery-passing portion of the measurement site, and wherein the pressing member includes a belt to be worn to wrap the measurement site in the circumferential direction, and a bag-shaped pressing cuff disposed to face an inner circumferential surface of the belt and extending along the circumferential direction to receive a supply of a pressurizing fluid and compress the measurement site.
 6. The sphygmomanometer according to claim 5, comprising a main body equipped with a pump, wherein the belt extends from the main body.
 7. The sphygmomanometer according to claim 6, wherein the pressing cuff, the back plate, and the sensing cuff constitute a cuff structure having a strap shape and one end attached to the main body, and wherein the cuff structure further includes a curler for keeping a shape of the cuff structure in a natural state curved along the circumferential direction along an outer circumferential surface of the pressing cuff.
 8. The sphygmomanometer according to claim 7, wherein a root portion on the main body side of the curler forming the one end of the cuff structure is sandwiched between a member disposed in the main body and a back lid of the main body, so that the one end of the cuff structure is attached to the main body.
 9. The sphygmomanometer according to claim 7, wherein the other end of the cuff structure on the side opposite to the one end is a free end.
 10. The sphygmomanometer according to claim 6, comprising a pressurization control part providing a control of compressing the measurement site by the pressing member via the sensing cuff, and a fluid storage control part providing a control of supplying and storing the pressure-transmitting fluid into the sensing cuff in a worn state in which the pressing member and the sensing cuff are worn on the measurement site, wherein the main body is equipped with a first flow path connecting the pump and the pressing cuff to allow a fluid to flow therebetween, and a second flow path connecting the pump or the first flow path and the sensing cuff to allow a fluid to flow therebetween and having an on-off valve interposed therein, wherein in the worn state, the fluid storage control part brings the on-off valve into an opened state and supplies and stores the pressure-transmitting fluid from the pump or the first flow path through the second flow path into the sensing cuff, and wherein after the pressure-transmitting fluid is stored in the sensing cuff, the pressurization control part brings the on-off valve into a closed state and supplies the pressurizing fluid from the pump through the first flow path to the pressing cuff to compress the measurement site.
 11. The sphygmomanometer according to claim 10, wherein the main body is equipped with the pressurization control part, the fluid storage control part, and the blood-pressure calculating part.
 12. A blood-pressure measurement method of measuring a blood pressure of a measurement site, including a bag-shaped sensing cuff to be worn to wrap the measurement site, a back plate disposed on the sensing cuff along a surface opposite to the measurement site and including, regarding a longitudinal direction perpendicular to a circumferential direction of the measurement site to be wrapped by the sensing cuff, a surface facing the measurement site in edge potions on both sides in a width direction along the longitudinal direction and curved in a direction away from the measurement site toward tips with the edge portions on both sides respectively gradually becoming thinner toward the tips, and a pressing member for pressing the back plate toward the measurement site, wherein the back plate is pressed toward the measurement site by the pressing member, and wherein the blood pressure is calculated based on a pressure of the fluid stored in the sensing cuff.
 13. A device comprising: a blood-pressure measurement element, wherein the blood-pressure measurement element includes a bag-shaped sensing cuff to be worn to wrap a measurement site; a back plate disposed on the sensing cuff along a surface opposite to the measurement site; a pressing member for pressing the back plate toward the measurement site; and a blood-pressure calculating part calculating a blood pressure based on a pressure of a fluid stored in the sensing cuff, wherein regarding a longitudinal direction perpendicular to a circumferential direction of the measurement site to be wrapped by the sensing cuff, a surface facing the measurement site in edge potions on both sides in a width direction along the longitudinal direction of the back plate is curved in a direction away from the measurement site toward tips with the edge portions on both sides respectively gradually becoming thinner toward the tips. 